Electrostatic recording head, a method for manufacturing the same, and an apparatus for practicing this method

ABSTRACT

An electrostatic recording head has a plurality of electrode wires arranged parallel to each other at a predetermined pitch to form recording electrodes at one ends thereof, control electrodes arranged along these recording electrodes, and a recording electrode retainer for integrally fixing these electrodes with a resin. The other ends of these electrode wires are integrally fixed by an electrode wire terminal end retainer of a resin. The electrode wires are electrically connected to a part of the conductive pattern formed on a printed circuit board interposed between both retainers, and are grouped thereby to form a plurality of recording electrode set conductors. These conductors and lead wires connected to the control electrodes are connected to connector terminals. A recording voltage is applied to the connector terminals.

BACKGROUND OF THE INVENTION

The present invention relates to an electrostatic recording system and,more particularly, to a multistylus type electrostatic recording headwhich is suitable for recording of image signals for a facsimile,printer or the like, a method for manufacturing the same, and anapparatus for practicing this method.

Various multistylus type electrostatic recording heads are known forelectronically scanning image signals to be recorded. An electrostaticrecording head for a facsimile is generally of a multistylus typewherein a number of recording electrodes which hold one-to-onecorrespondence with all the picture elements corresponding to onescanning line are arranged in an array in an insulator such as an epoxyresin mold. Auxiliary electrodes arranged on the front or back surfaceside of the recording medium closely contacted with the recording headhelp to perform electronic scanning of image signals of a recordingmedium.

FIG. 1 is a schematic perspective view of a conventional electrostaticrecording head of the single surface control type wherein recordingelectrodes and auxiliary electrodes are arranged on the same surfacewith respect to the recording medium. A number of recording electrodes10 are independently embedded at a pitch of several electrodes permilimeter in an electrode retainer 12 of an insulator such as an epoxyresin. Front ends of the recording electrodes 10 are exposed to thesurface of the retainer 12. Auxiliary electrodes 14 are also embedded inthe electrode retainer 12 at both sides of the recording electrodes 10and on the same plane as the recording electrodes 10. The auxiliaryelectrodes 14 are also exposed to the surface of the retainer 12. Theauxiliary electrodes 14 divide the recording electrodes 10 into groupsof equal numbers and are arranged in correspondence with the respectivegroups. The auxiliary electrodes 14 serve to control the recordingpositions of the recording electrodes 10 and are thus also calledcontrol electrodes. Electrostatic recording is performed by dividing arecording voltage into two voltages which are applied to the recordingelectrodes 10 and the control electrodes 14. Then, recording isperformed only at positions on an electrostatic recording paper sheet 16where both voltages are applied simultaneously.

The recording mechanism of the electrostatic recording head of thesingle surface type of the electrode arrangement as described above willnow be described with reference to FIG. 2. Referring to FIG. 2, a numberof recording electrodes 10 are divided into a number of electrode groupseach consisting of m recording electrodes 10. Then, the recordingelectrodes at the same positions in every other group are connected toeach other to provide two systems GA and GB of electrode groups. Therecording electrodes of each electrode group are arranged to extend fromthe center of the corresponding control electrode 14 to the center ofthe adjacent control electrode 14. With the electrode arrangement shownin FIG. 2, if the numbers of the recording electrodes 10 and the controlelectrodes 14 are respectively N and M, the following relation is held:

    M=(N/m)+1

Electrostatic recording is simultaneously performed with m recordingelectrodes of each group. The control electrodes 14 are used to selectthe electrode groups for recording. More specifically, referring to FIG.2, in order to record with a first electrode group G-1, 0 V and a highvoltage such as -300 V which alone may not effect formation of anelectrostatic latent image are applied, in accordance with the patternto be recorded, to the system GA of the electrode groups.Simultaneously, a voltage which has substantially the same absolutevalue as the above-mentioned voltage and which has the opposite polaritythereto, for example +300 V, is applied to the first and second controlelectrodes of a system GC of the control electrodes 14. Then, apotential difference of 600 V or 300 V is established between therecording electrodes of the first electrode group G-1 and theelectrostatic recording paper sheet (not shown). An electrostatic latentimage is formed on the surface of the electrostatic recording papersheet immediately below the recording electrodes at which the potentialdifference of 600 V is established. Next, the system GB of the recordingelectrodes is driven while applying a voltage to the second and thirdcontrol electrodes. Thus, recording with the second electrode group G-2is performed. Thereafter, scanning and recording of one line isperformed by applying a voltage to two control electrodes while shiftingone control electrode at a time and while alternately driving the systemGA and GB of electrode groups.

In this manner, the recording electrode groups are divided into twosystems and are alternately driven. Two control electrodes aresimultaneously driven. This is to prevent a drop in the potentialdistribution of the electrostatic recording paper sheet 16 at the edgesof the control electrodes 14 as indicated by the dotted lines in FIG. 3.With this arrangement, a substantially flat potential distribution asindicated by a solid line is obtained even at the edges of the controlelectrode 14. Then, an electrostatic latent image which is uniform inthe scanning direction can be formed. In the arrangement shown in FIG.1, the control electrodes 14 are arranged at both sides and in thevicinities of the recording electrodes 10. This is also for the purposeof obtaining a flat potential distribution of the electrostaticrecording paper sheet 16 at the positions of the recording electrodes10. Referring to FIG. 1, the control electrodes 14 at both sides of onerecording electrode 10 are commonly connected.

FIG. 4 schematically shows the structure of a conventional electrostaticrecording head having the electrode arrangement shown in FIG. 2.Referring to FIG. 4, electrode wires 18 corresponding to the recordingelectrodes shown in FIGS. 1 and 2 comprise, for example, nickel wireshaving a diameter of 0.04 to 0.1 mm and covered with a polyurethanelayer. One ends each of the electrode wires 18 are embedded in arod-shaped electrode retainer 12 of an insulator such as an epoxy resin.One ends of these electrode wires 18 are exposed to the surface of theretainer 12 in the longitudinal direction thereof to constitute therecording electrodes 10. The electrode wires 18 correspondent to eachrecording electrode 10 are divided into electrode groups each consistingof m electrodes. The electrode wires 18 at the same positions in eachelectrode group are commonly connected to define electrode wire sets 20numbering 2m. Each electrode wire set 20 belongs to either of thesystems GA and GB of the recording electrode groups. The electrode wiresets 20 are connected to the upper portion of a printed circuit board 22to be connected to a recording electrode drive circuit (not shown)through connectors 24. High voltage pulses are thus applied to theelectrode wire sets 20 in accordance with the image signals to berecorded.

Meanwhile, the control electrodes 14 of rectangular shape are embeddedin the electrode retainer 12 in a similar manner to that of therecording electrodes 10. One ends each of the control electrodes 14 arearranged close to both sides of the associated recording electrodes andwithin the same plane of the recording electrodes. The controlelectrodes 14 are connected to the front and back surfaces of theprinted circuit board 22 through lead wires 26, respectively. Thecontrol electrodes 14 of each pair opposing each other with theassociated recording electrode therebetween are commonly connected bythrough holes. The control electrodes 14 are connected to a controlelectrode drive circuit (not shown) through the connectors 24 of theprinted circuit board 22. Thus, high voltage pulses of opposite polarityto that of a voltage applied to the recording electrodes are applied tothese control electrodes so as to control the recording position.

Although not shown in the figure, the electrode retainer 12 and theprinted circuit board 22 are fixed by a casing to constitute anelectrostatic recording head unit.

With a conventional electrostatic recording head of the configuration asdescribed above, wiring of the recording electrodes or electrode wiresis extremely complex. Specifically, the electrode wires 18 constitutingthe recording electrodes 10 shown in FIG. 4 must be grouped and those atthe same positions of each group must be commonly connected to form theelectrode wire sets 20. During such operation, it is extremely difficultto correctly group a great number of thin electrode wires according totheir positions and orders. Moreover, connection of the electrode wiresduring wiring of the electrode wire sets is not easy either. Manufactureof such an electrostatic recording head thus requires much skill, andinspection and correction of erroneous connection is also extremelydifficult.

The electrode wires 18 are arranged in a very complex manner and are incontact with each other after formation of the electrode wire sets 20.Although these electrode wires 18 are insulated, relatively highvoltages applied to them can invite dielectric breakdown. Impact orvibration can also cause damage to them. The conventional electrostaticrecording head as described above thus has problems of stability andreliability.

Another electrostatic recording head is also known which utilizes aprinted circuit board of a different configuration. This printed circuitboard is obtained by forming by photoetching on a copper-platedlaminate, recording electrodes which are formed by photoetching, and amatrix circuit for forming electrode sets by commonly connecting therecording electrodes at the same positions of a number of electrodegroups. With this arrangement, a highly advanced technique is requiredin order to manufacture recording electrodes which are arranged at ahigh pitch. The manufacturing yield of such heads is low andmanufacturing cost is high. Since the recording electrodes are formed byphotoetching a copper-plated laminate, the recording electrodes becomesmaller than those formed from electrode wires of the prior art asdescribed above. The recording electrodes also become asymmetrical withrespect to the center (for example, trapezoidal). When such recordingelectrodes are used for facsimile or the like, recording reliability anddensity are degraded.

As has been described above, in the conventional head shown in FIG. 1,the control electrodes 14 are embedded and exposed through the electroderetainer 12 together with the recording electrodes 10. These controlelectrodes 14 are manufactured in the manner as shown in FIG. 5.Specifically, a square bar 28 is milled to form teeth 30. The lead wires26 are connected to these teeth 30 to form a control electrode element.A pair of control electrode elements is prepared. This pair of controlelectrode elements is integrally formed with a resin with electrodewires or recording electrodes therebetween. Thereafter, the integralbody obtained is cut at dotted lines in FIG. 5.

With such a manufacturing method, milling takes time and increases thenumber of manufacturing steps, so that the manufacturing cost isincreased.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a electrostaticrecording head with a novel structure which is easy to manufacture, amethod for manufacturing the same, and an apparatus for practicing thismethod.

It is another object of the present invention to provide anelectrostatic recording head with improved reliability and stability, amethod for manufacturing the same, and an apparatus for practicing thismethod.

It is still another object of the present invention to provide anelectrostatic recording head which does not require a highly advancedprinted circuit board manufacturing technique and which is excellent inrecording characteristics, a method for manufacturing the same and anapparatus for practicing this method.

It is still another object of the present invention to provide anelectrostatic recording head which is inexpensive to manufacture, amethod for manufacturing the same, and an apparatus for practicing thismethod.

The above and other objects have been attained by an electrostaticrecording head which comprises: a recording electrode retainer in whicha plurality of electrode wires are arranged parallel to each other at apredetermined pitch, said plurality of electrode wires constitutingrecording electrodes at one ends each thereof, in which controlelectrodes are arranged along said recording electrodes, and in whichsaid recording electrodes and said control electrodes are integrallyformed and fixed with a resin; an electrode wire terminal end retainerof a resin for fixing the other ends of said electrode wires at a pitchthe same as the pitch of said recording electrodes; and a printedcircuit board interposed between said recording electrode retainer andsaid electrode wire terminal end retainer, on said printed circuit boardbeing formed electrode wire connecting lands at positions correspondingto said electrode wires, conductors for forming recording electrode setsby connecting said electrode wire connecting lands corresponding to saidelectrode wires of said recording electrodes at the same relativepositions in a plurality of groups of said electrode wire connectinglands formed in correspondence with groups of said recording electrodes,and lead wire connecting lands to be connected to lead wires which are,in turn, connected to said control electrodes, said printed circuitboard having connector terminals to be connected to said recordingelectrode set conductors and said lead wire connecting lands, saidelectrode wires being connected to corresponding ones of said electrodewire connecting lands, and said lead wires being connected tocorresponding ones of said lead wire connecting lands.

With the arrangement of the present invention as described above, thefollowing advantages are obtained as compared with the conventionalapparatus.

The arrangement of the printed circuit board and the electrode wiresconstituting the recording electrodes is orderly and suitable forautomatic operation. Therefore, most part of the work which has beenconventionally manually performed can be automatically performed,resulting in significant labor savings. Furthermore, the arrangement ofthe present invention does not involve irregular wiring, so thaterroneous wiring may be reduced to the minimum and wiring inspection maybe simplified. The electrode wires are all fixed to the printed circuitboard in an orderly manner and the terminal ends of the electrode wiresare fixed to the electrode wire terminal end retainer. Thus, theelectrode wires do not cross each other as in the conventionalarrangements. Therefore, the dielectric breakdown may not be caused, anddamage due to vibration and impact may be reduced to the minimum. Withthese advantages, an electrostatic recording head which is improved inreliability and stability is provided. Furthermore, since the terminalends of a number of electrode wires are retained by the electrode wireterminal end retainer, handling of the terminal ends of the electrodewires is simpler than with the conventional arrangements. A conventionalelectrostatic recording head uses a printed circuit board on whichrecording electrodes and a matrix circuit are simultaneously formed byphotoetching a copper-plated laminate. In comparison with thisconventional electrostatic recording head, an electrostatic recordinghead of the present invention uses a printed circuit board which doesnot require advanced manufacturing techniques. Therefore, with thearrangement of the present invention, the manufacturing cost is lower,and the recording quality and density are improved since recordingelectrodes have circular cross-sectional shapes of constant size.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example and to make the description clearer, reference is madeto the accompanying drawings in which:

FIG. 1 is a schematic perspective view of part of a conventionalelectrostatic recording head of the single surface control type;

FIG. 2 is a view showing the arrangement of the electrodes of theelectrostatic recording head shown in FIG. 1;

FIG. 3 is a view showing the mode of operation of the control electrodesshown in FIG. 2;

FIG. 4 is a schematic perspective view showing the arrangement of theconventional electrostatic recording head of the single surface controltype;

FIG. 5 is a view for explanation of the manufacturing method of thecontrol electrodes;

FIG. 6 is a schematic perspective view showing the arrangement of anelectrostatic recording head of the single surface control typeaccording to the first embodiment of the present invention;

FIG. 7 is a schematic view showing a printed circuit board used in thehead shown in FIG. 6;

FIG. 8 is a schematic perspective view showing the arrangement of anelectrostatic recording head of the single surface control typeaccording to the second embodiment of the present invention;

FIG. 9 is a schematic view showing a flexible printed circuit board usedin the head shown in FIG. 8;

FIG. 10 is a schematic view showing a modification of the flexibleprinted circuit board shown in FIG. 9;

FIG. 11 is a schematic view showing an apparatus for manufacturing theelectrostatic recording head shown in FIG. 8, according to the thirdembodiment of the present invention;

FIG. 12 is a schematic perspective view of an insulating film removingapparatus shown in FIG. 11;

FIG. 13 is a schematic perspective view of a control electrode unit usedin the electrostatic recording head shown in FIG. 8;

FIG. 14 is a view for explanation of a method for manufacturing an arrayof control electrodes used in the electrostatic recording head shown inFIG. 8; and

FIG. 15 is a view for explanation of a method for manufacturing theelectrostatic recording head shown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings. FIG. 6 is a schematicperspective view of an electrostatic recording head according to thefirst embodiment of the present invention. The arrangement and wiring ofrecording electrodes 32 and control electrodes 34 of the electrostaticrecording head shown in FIG. 6 are the same as those of the conventionalhead shown in FIG. 2.

Electrode wires 36 shown in FIG. 6 are obtained by coating wires ofcopper, nickel or phosphor bronze and of 0.04 to 0.1 mm diameter with auniform insulating film of 5 to 20 μm thickness and of formal,polyurethane or polyester. One ends each of these electrode wires 36 areembedded in a rod-shaped electrode retainer 38 of an insulator such asan epoxy resin. End faces of the electrode wires 36 are exposed to thesurface of the electrode retainer 38 in an array at a predeterminedpitch (0.06 to 0.2 mm) along the longitudinal direction of the retainer,thereby defining the recording electrodes 32. The recording electrodes32 are thus positioned to be brought into contact with a recordingmedium. As will be described in further detail later, the other ends ofthe electrode wires 36 are completely embedded in an electrode wireterminal retainer 40 of the same insulator as that of the electroderetainer 38 or a similar insulator at the same pitch as that of therecording electrodes 36. The other ends of the electrode wires 36 arenot exposed to the surface of the electrode wire terminal retainer 40.The electrode wires 36 between the electrode retainer 38 and theelectrode wire terminal end retainer 40 extend at the same pitch as thatof the recording electrodes as shown in FIG. 6 and are respectivelyelectrically connected to predetermined positions of a printed circuitboard 42.

The printed circuit board 42 is used to realize the arrangement of therecording electrodes of the electrostatic recording head shown in FIG.2. Specifically, the recording electrodes 32 are divided into a numberof electrode groups each consisting of m recording electrodes; wiringfor connecting the recording electrodes 32 at the same positions inevery other electrode group to provide two systems GA and GB ofrecording electrodes is formed by photoetching a copper-plated laminate.

The printed circuit board 42 will be described in further detail withreference to FIG. 7.

Electrode wire connecting lands 44 for electrically connecting theelectrode wires 36 shown in FIG. 7 are formed at a constant pitch and ina staggered form in correspondence with the recording electrodes 32 orthe electrode wires 36 to facilitate grouping thereof. These electrodewire connecting lands 44 are arranged parallel to an array of recordingelectrodes and are arranged in arrays each consisting of a predeterminednumber, for example, twice the number m of the recording electrodes inthe electrode group or 2m. The electrode wire connecting lands 44 areconnected by conductors 46 so as to connect the recording electrodes orelectrode wires 36 at the same relative positions in every otherrecording electrode group. The recording electrode sets defined by theseconductors 46 are connected to a recording electrode drive circuit whichsupplies thereto a high voltage pulse corresponding to an image signalto be recorded, as has been described above. These conductors 46 areelectrically connected to conductors 50 at the rear surface of the boardvia through holes 48 formed at parts of the electrode wire connectinglands 44 or parts of the conductors 46. The conductors 50 are thenconnected to connectors 52₁ for connection with the recording electrodedrive circuit (not shown). The printed circuit board 42 further has leadwire connecting lands 56 for connecting lead wires 54 to be connected tothe control electrode 34, and conductors 60 for connecting lands 56 toconnectors 52₂. The control electrodes 34 are embedded in the electroderetainer 38 shown in FIG. 6 and exposed to the same surface of therecording electrodes, so as to control the recording positions of therecording electrodes.

Referring to FIG. 7, a description has been made on the printed circuitboard 42 which integrally incorporates the connectors, the matrixcircuit for grouping the recording electrodes and the lead wireconnecting lands for the control electrodes. However, they may be ofseparate arrangements. For example, as shown in FIG. 8, a flexibleprinted circuit board 62 may be provided for the matrix circuit, and arigid printed circuit board 62 may be provided for the rest of thecircuitry. These two printed circuit boards may then be integrallyformed for electrical connection therebetween. FIG. 8 shows a schematicperspective view of an electrostatic recording head of this type, andFIG. 9 shows a schematic view of the flexible printed circuit board usedfor the electrostatic recording head shown in FIG. 8.

The flexible printed circuit board 62 shown in FIG. 9 is made of aflexible laminate of polyester, polyimide, glass epoxy with a thicknessof 25 to 125 μm. The configuration of this printed circuit board 62consisting of the lands 44, the conductors 46 and the conductors 50 isthe same as that of the printed circuit board 42 shown in FIG. 7 exceptfor terminals 66. A printed circuit board 68 as shown in FIG. 10 mayalternatively be provided wherein the number of electrode wireconnecting lands in an array equals m, the number of the recordingelectrodes in one electrode group, in order to make the size of theboard along the direction of the electrode wires smaller and to therebyobtain a more compact electrostatic recording head. Referring to FIG.10, every other electrode wire connecting lands 70 in each array arecommonly connected by conductors 72. The terminals 66 are used forelectrical connection of the flexible printed circuit board 62, 68 withthe rigid printed circuit board 64 having the connectors and the leadwire connecting lands. The flexible printed circuit board 62, 68 and therigid printed circuit board 64 have terminals of substantially the samenumber and shape, and are electrically connected to each other by mutualcontact, adhesion with an electrically conductive adhesive, orsoldering. The flexible printed circuit board is used due to ease inmanufacture.

FIG. 11 shows an embodiment of an apparatus for manufacturing theelectrostatic recording head shown in FIG. 8. On the outercircumferential surface of a metal column or cylinder (to be referred toas a winding drum hereinafter) 80 having a diameter of about 100 mm areformed thread grooves 82 at the same pitch of the recording electrodes,for example, 0.125 mm. A relatively deep straight groove 84 and arelatively shallow straight groove 86 are formed by an angular intervalof about 180° along the longitudinal direction of the winding drum 80 tocross the thread grooves 82. The winding drum 80 has shafts at its endsso as to be driven by a power source (not shown) in the directionindicated by arrow A1. A metal column (to be referred to as a guidescrew) 88 of small diameter is also rotated at the same speed as that ofthe winding drum 80 in the direction indicated by arrow A2 through atransmission mechanism (not shown). Thread grooves 90 are formed on theouter circumferential surface of the guide screw 88 at the same pitch ofthe thread grooves 82. Wire guides 92 and 94 for guiding an electrodewire 96 are rotatably supported. An insulating film removing apparatus98 to be used in the present invention drives an electrode wire 96 andremoves the insulating film at part of the wire for a predeterminedlength. FIG. 12 is a schematic perspective view of the insulating filmremoving apparatus 98. The insulating film removing apparatus 98 shownin FIG. 12 is of the type wherein the insulating film is burnt away bythe flame of a small torch. A small flame 100 is obtained by burning agas mixture of hydrogen and oxygen which is sprayed out of a nozzle 102having a small inner diameter. A tube 104 of small diameter fitted andfixed by a bush 112 which is, in turn, fixed to an operation lever 110rotatably supported by a pin 108 of a rotary lever 106. The rotary lever106 also has an single-turn clutch 114 and pulley 116 an the same shaftand is intermittently driven by a power source (not shown). The pulley116 is constantly rotated by the power source (not shown). Thesingle-turn clutch 114 is normally in the off state, and the front endof an armature 120 of an electromagnetic solenoid 118 is fitted in thehole formed in the single-turn clutch 114. When the electromagneticsolenoid 118 is temporarily driven to disengage the armature 120 fromthe single-turn clutch 114, the single-turn clutch 114 is placed in theon state during one revolution, and the rotary lever 106 rotates once.One end of the tube 104 is fitted and slidably supported by a slide bush126 which is, in turn, fixed to a pivot lever 124 rotatably supported bya pin 122. This end of the tube 104 is connected to a rubber tube 128 tobe supplied with a gas mixture of hydrogen and oxygen from a gas source(not shown).

The mode of operation of the insulating film removing apparatus 98 ofthe construction as described above will now be described with referenceto FIG. 12.

The small flame 100 prior to the insulating film removing operation isat the lowermost position of a movement track 130 as shown in FIG. 12.Meanwhile, the electrode wire 96 from which the insulating film must beremoved is travelling at a predetermined speed in a direction indicatedby arrow while keeping a predetermined angle θ smaller than 90° withrespect to the movement track 130. The pulley 116 is driven by powertransmitted through a belt or chain from the power source (not shown).When the single-turn clutch 14 is triggered at a predetermined timing,the rotary lever 106 rotates once. Then, since the lower end of the tube104 slides within the slide bush 126 and pivots transversely with thepivot lever 124, the upper end thereof moves elliptically together withthe operation lever 112 and the bush 112. The small flame 100 above thenozzle 102 moves on the elliptical movement track 130 in the directionindicated by arrow. At the upper, substantially linear part of thetrack, the small flame crosses the electrode wire 96 at a skew angle θto remove the insulating film on the wire. The speed of the small flameand the angle θ of the small flame with respect to the electrode wireare suitably selected so that the insulating film may be removed for adesired length without the electrode wire being melted.

A further description will be made referring back to FIG. 11. A tensioncontrol mechanism 132 for the electrode wire shown in FIG. 11 isincorporated for damping, at a constant torque with a hysteresis brakeor the like, the rotation of the winding drum 80 on which several turnsof the electrode wire are wound. The mechanism 132 is thus used forcorrectly winding the electrode wire 96 on the winding drum 80. Thetension control mechanism 132, the insulating film removing apparatus98, and the wire guides 92 and 94 are arranged on a table 134. Thistable 134 is provided so as to be movable parallel (e.g., directionindicated by arrow B) to the longitudinal direction of the winding drumin synchronism with the rotation of the winding drum 80 by driving afeed screw 136 by a power source (not shown). Wire guides 138, 140 and142 are used to guide and switch the travelling direction of theelectrode wire 96 and are rotatably supported. A buffer roll 144 isrotatably supported by a buffer lever 148 which is supported to bepivotal about a pin 146. The buffer roll 144 adjusts the tension actingon the electrode wire 96 which is exerted by a tension spring 150. Awire spool 152 is rotatably supported and continuously supplies theelectrode wire 96.

The method for manufacturing the electrostatic recording head shown inFIG. 8 using the apparatus shown in FIG. 11 will now be described.

Prior to arranging the electrode wire, one array of the controlelectrodes of the two arrays sandwiching the recording electrodes 32shown in FIG. 8 is mounted on the straight groove 84 of the winding drum80. The flexible printed circuit board shown in FIG. 9 or 10 is woundand fixed at a predetermined position of the winding drum 80. On thelands 44 and 70 of this flexible pitch circuit board is printed an epoxyresin, containing an electrically conductive adhesive such as a silverfiller which has some fluidity at room temperature, to a predeterminedthickness by a suitable means such as screen printing process. A controlelectrode unit 166 consisting of a rod-shaped portion 160 having a crosssection of a predetermined area, a conductive wire portion 162 connectedthereto and of smaller cross-sectional area, and a flat portion 164 forconnection with the lead wire as shown in FIG. 13 is manufactured bycold working or the like of brass or phosphor bronze wire. End faces ofthe rod-shaped portions of a predetermined number of such controlelectrode units 166 are adhered or welded to a flat plate 168 at a pitchthe same as that of the control electrodes, as shown in FIG. 14. Anarray of the control electrodes is thus obtained. After injection of anepoxy resin, the array is cut at the dotted lines to provide separatecontrol electrodes.

According to the method wherein the control electrode units havingrod-shaped portions at least at one ends thereof are arranged on andadhered to a flat plate and then injected with a resin, the number ofmanufacturing steps is significantly reduced than with the conventionalmethod wherein a square bar is sliced to provide control electrodeelements. Therefore, an inexpensive electrostatic recording head may bemanufactured. With a control electrode unit which has a lead-wireconnecting portion in addition to the rod-shaped portion, the lead wiremay be connected to the lead-wire connecting portion extending from therod-shaped portion. Therefore, connection of the lead wire is easierthan with the unit in which the lead wire must be connected verticallyto the flat surface.

The electrode wire 96 is supplied from the wire spool 152 and passedthrough the wire guide 142 and 140, the buffer roll 144, and the wireguide 138. One end of the electrode wire 96 is fixed near the threadgroove 82 of the winding drum 80 through the tension control mechanism132, the insulating film removing apparatus 98, and the guide screw 88.The winding drum 80 and the guide screw 88 are rotated at the same speedin the direction indicated by arrow in this condition, and the table 134is moved in synchronism with this rotary movement. The insulating filmremoving apparatus 98 operates for every revolution of the winding drum80 so that the parts of the electrode wire 96 from which the insulatingfilm is removed may be brought into contact with the lands 44 and 70 ofthe flexible printed circuit board. In this manner, a predeterminedtension is exerted on the electrode wire 96 by the tension controlmechanism 132, the insulating film at a predetermined portion of thewire is removed, and the wire is guided by the guide screw 88 to bewound on the screw grooves 82 of the winding drum 80. During thiswinding operation, all the electrode wires 96 for the recordingelectrodes are connected to the flexible printed circuit board. Thiswill be described in further detail with reference to FIG. 15.

FIG. 15 shows part of the flexible printed circuit board 62. Referencenumerals 96, 44 and 46 respectively denote the electrode wire, theelectrode wire connecting lands, the conductors for matrix wiring of thelands. The electrode wires 96 wound around the winding drum 80 arearranged at a pitch p same as that of the recording electrodes, andcross the electrode wire connecting lands 44 which are formed in anorderly manner on the flexible printed circuit board 62. The insulatingfilm of the electrode wire 96 is removed at positions corresponding tothe electrode wire connecting lands by the insulating film removingapparatus 98. Specifically, the insulating film of the first electrodewire 96 is removed in correspondence with a land A . The insulating filmof the second electrode wire 96 is removed at a distance q from theremoved portion of the first electrode wire in correspondence with aland B . The land B at a distance q from the land A . The lands arestaggered by a distance q which is the same as the pitch of therecording electrodes so that the electrode wires to be connected areconstantly positioned at the centers thereof. In the same manner, theportions of the electrode wire from which the insulating film is removedand the lands are arranged in correspondence with each other.

As has been described above, on the lands 46 is applied the electricallyconductive adhesive in advance. The electrode wires from which theinsulating film has been removed are rendered electrically conductiveand mechanically strong after heating and hardening. Specifically, theelectrical connection between the electrode wires and the lands isaccomplished with an electrically conductive adhesive applied to certainportions of the lands or by low-temperature soldering. The electricallyconductive adhesive is, for example, an epoxy resin containing a silverfiller. After heating and hardening, the adhesive achieves electricalconduction and mechanically fixes the electrode wires 96 to the printedcircuit board 62. Although the electrically conductive adhesive coversadjacent wires, these wires may not be electrically connected to theelectrode wire connecting land nearby since these wires are stillcovered with the insulating film. Therefore, only the electrode wiresfrom which the insulating film has been removed in correspondence withthe lands are electrically connected therewith. A solder to be used inthis case is a solder which melts at a temperature at which theinsulating film may not melt and serves the same purpose as theelectrically conductive adhesive. It is also possible to select theelectrode wires and directly connect the selected electrode wires to thelands by a welder which uses a laser.

When the electrode wires are arranged to constitute all the recordingelectrodes 32 of the electrostatic recording head shown in FIG. 8, thewinding drum 80 and the table 134 stop rotating and the insulating filmremoving apparatus 98 stops operating. The electrode wire 96 is cut andthe terminal end thereof is fixed to the winding drum. Thereafter, thewinding drum 80 is removed from the apparatus shown in FIG. 11. Moldshaving grooves corresponding to the depths of the grooves 84 and 86 aremounted to the winding drum 80. An epoxy resin is injected into themolds to form the electrode retainer 38 shown in FIG. 8 at the partcorresponding to the relatively deep straight groove 84 and to form theelectrode wire terminal end retainer 40 at the part corresponding to therelatively shallow straight groove 86. The array of the controlelectrodes shown in FIG. 14 is mounted to a predetermined position ofthe mold for the relatively deep straight groove 84 for the purpose offorming the other array of control electrodes as in the case of thegroove 84 prior to the winding operation described above.

The winding drum 80 after molding is heated at a predeterminedtemperature for a predetermined period of time and is thereafter cooled.By this heat treatment, the electrode wires and the control electrodesare formed integrally with each other. Simultaneously, the electricallyconductive adhesive applied on the electrode wire connecting lands ofthe flexible printed circuit board is hardened to securely fix theelectrode wires and to electrically connect the lands with the electrodewires. After unnecessary portions of the electrode wires are cut awayand the molds and winding drum are removed, the electrode retainer 38and the electrode wire terminal end retainer 40 are machined topredetermined sizes. An insulator such as a resin is applied to thesurface of the electrode wire terminal end retainer 40 to which the endfaces of the electrode wires are exposed, thereby completely insulatingand embedding the ends of the electrode wires. The flexible printedcircuit board 62 to which are fixed the electrode wires 36 constitutingthe recording electrodes 32 is integrally formed, by welding bysoldering or adhesion with an electrically conductive adhesive, with therigid printed circuit board 64 having the lead wire connecting lands forthe control electrodes 34 and the connectors 74 for connection with thedrive circuit (not shown) for driving the electrodes. The lead wires 54are suspended between flat portions 164 (FIG. 13) of the controlelectrodes and the rigid printed circuit board 64, and soldered toprovide the electrostatic recording head as shown in FIG. 8. Althoughnot shown, the electrode retainer 38 and the rigid printed circuit board64 of the electrostatic recording head are fixed by metal members andcovered, and are thereafter assembled in an electrostatic recordingapparatus such as a facsimile.

Various other changes and modifications may be made within the spiritand scope of the present invention.

What we claim is:
 1. An electrostatic recording head comprising:aplurality of recording electrode wires arranged in parallel withconstant intervals therebetween in a first plane, each of said recordingelectrode wires having one end surface establishing a recording headelectrode and being coated with a meltable insulating layer with part ofsaid meltable insulating layer being melted; a plurality of controlelectrode wires arranged in parallel at constant intervals therebetweenin a second plane, said second plane being parallel and close to saidfirst plane of said recording electrode wires, said intervals of saidcontrol electrode wires being greater than said intervals of saidrecording electrode wires, each of said control electrode wires havingone end surface establishing a control electrode, and said controlelectrodes and recording head electrode defining a third plane; and aprinted circuit board including a plurality of printed lands connectedto the respective recording electrode wire at said part of said meltableinsulting layer which is melted, a plurality of printed conductors forconnecting those printed lands which are connected to everypredetermined number of recording electrode wires, and connectors eachof which is connected to a respective one of said printed conductors. 2.An electrostatic recording head according to claim 1, wherein saidprinted lands are arranged in a matrix form on said printed circuitboard, with said predetermined number being as the number of rows of thematrix, in such a manner that with lands in each row are staggered by apitch of said electrode wires from the corresponding lands in theadjacent row, said rows of the matrix being parallel to said recordingelectrode line.
 3. An electrostatic recording head according to claim 2,wherein said lands in each row are connected through said printedconductors.
 4. An electrostatic recording head according to claim 2,wherein every other one of said lands in each row is connected throughsaid printed conductors.
 5. An electrostatic recording head according toclaim 1, wherein said printed circuit board comprises a first section onwhich said lands are provided and a second section on which saidconnectors are provided.
 6. An electrostatic recording head according toclaim 5, wherein said first section and said second section are rigidprinted circuit boards.
 7. An electrostatic recording head according toclaim 5, wherein said first section is a flexible printed circuit boardand said second section is a rigid printed circuit board.